作用
1． 作狀語
1) 表示時間 如：
Her homework done (=After her homework was done),Lucy decided to go shopping.
2) 表示原因 如：
There being no buses (Because there were no buses),we had to walk home.
3) 表示條件 如：
Weather permitting (If weather permits), we will go to play football.
4) 表示方式或伴隨 如：
He rushed into the room, his face covered with sweat.
2． 作同位語 如：
There are two doors, one leading to the bedroom, the other (leading) to the kitchen.
